The ultimate goal of the experiments in this proposal is to define components that play a role in regulating the stability and translation of "pattern-determining" mRNAs, and to understand the importance of these post-transcriptional events for embryonic development. Unlike the typical housekeeping gene, genes involved in the determination of the Drosophila body plan are frequently regulated at multiple levels to attain their temporal and spatial pattern of expression. For instance, accumulation of bicoid protein is inhibited during oogenesis, presumably to avoid premature initiation of the embryonic developmental program. The bicoid mRNA is stable and is translated during the first few hours of embryogenesis establishing a gradient of bicoid protein that activates downstream genes. At the onset of gastrulation this mRNA is quickly degraded, presumably to turn off the genes it had earlier activated. The fushi tarazu (ftz) mRNA is unstable in the embryo, even at times when bicoid mRNA is stable, indicating that the stability of ftz and bicoid are regulated by different mechanisms. The ftz mRNA instability is believed to be essential for establishment of its striped pattern of expression. The experiments have the following objectives. i) Previous work from this laboratory indicated that a gene (termed gene R) located in chromosome 3R is required zygotically for the destabilization of bicoid mRNA around the time of gastrulation. A major goal of the present experiments is to genetically identify gene R by mutational analysis. ii) Gene R will be cloned and this will be followed by experiments to investigate the mechanism of its action. iii) Cis-acting sequences that signal destabilization of bicoid mRNA will be identified. iv) Mechanisms that prevent bicoid protein from accumulating during oogenesis will be investigated by studying the expression of structurally altered bicoid genes. v) Sequences that serve as targets of ftz mRNA instability will be identified and the effects of mutationally stabilizing ftz mRNA on its spatial pattern of expression and on embryonic development will be assessed. Unstable mRNAs often encode products that are required in a temporally and/or spatially restricted manner. The proposed studies address the importance of post-transcriptional regulatory events for pattern formation during embryonic development. These findings may be of general relevance for understanding developmental mechanisms in other organisms, including mammals.